Jerry you should be able to go online and find the operators manual for your tiller and there should be instructions there.
I don't have my tiller manual with me but with my brand ( Taylor Way) you need to make certain you have 6" of overlap whenever the tiller is engaged. There is a method to determine where and how to measure based on when the tiller is closest and furthest from the Tiller.
You will need a saws-all with carbide tip to cut off the extra PTO shaft.
Sorry I couldn't be more help. Good luck!